System and method for additively manufacturing a composite structure

ABSTRACT

A system for additively manufacturing a composite part is disclosed. The system may include a vat configured to hold a supply of resin, and a build surface disposed inside the vat. The system may also include a print head configured to discharge a matrix-coated continuous reinforcement onto the build surface, and an energy source configured to expose resin on a surface of the matrix-coated continuous reinforcement to a cure energy.

RELATED APPLICATIONS

This application is based on and claims the benefit of priority fromU.S. Provisional Application No. 62/449,899 that was filed on Jan. 24,2017, the contents of which are expressly incorporated herein byreference.

TECHNICAL FIELD

The present disclosure relates generally to a manufacturing system andmethod and, more particularly, to a system and method for additivelymanufacturing a composite structure.

BACKGROUND

Many different processes of additive manufacturing are commonly used toproduce machine components. These processes may include, among others,Continuous Fiber 3D Printing (CF3D™) and Stereolithography (SLA).

CF3D™ involves the use of continuous fibers embedded within materialdischarging from a moveable print head. A matrix is supplied to theprint head and discharged (e.g., extruded and/or pultruded) along withone or more continuous fibers also passing through the same head at thesame time. The matrix can be a traditional thermoplastic, a powderedmetal, a liquid resin (e.g., a UV curable and/or two-part resin), or acombination of any of these and other known matrixes. Upon exiting theprint head, a cure enhancer (e.g., a UV light, an ultrasonic emitter, aheat source, a catalyst supply, etc.) is activated to initiate and/orcomplete curing of the matrix. This curing occurs almost immediately,allowing for unsupported structures to be fabricated in free space. Andwhen fibers, particularly continuous fibers, are embedded within thestructure, a strength of the structure may be multiplied beyond thematrix-dependent strength. An example of this technology is disclosed inU.S. Pat. No. 9,511,543 that issued to Tyler on Dec. 6, 2016 (“the '543patent”).

SLA also involves the use of a light-emitting device (e.g., a UV lightprojector, an electron beam emitter, or a laser). The light-emittingdevice is computer controlled to selectively energize a layer of resinwithin a vat in a particular pattern corresponding to an outline of apart. The resin (e.g., a liquid photo-polymerizing resin) solidifiesupon being energized, and a subsequent layer of resin within the tank isthem energized in a new pattern. This may continue, with the part beingincrementally raised out of or lowered further into the vat, until alllayers of the component have been fabricated. Parts produced via SLA mayhave high-resolution surface finishes.

Although parts fabricated via CF3D™ and SLA may have some desiredcharacteristics (e.g., high-strength and high-resolution, respectively),neither process alone may be able to provide all desired characteristicsof both processes. The disclosed system is directed at addressing one ormore of the problems set forth above and/or other problems of the priorart.

SUMMARY

In one aspect, the present disclosure is directed to an additivemanufacturing system. The additive manufacturing system may include avat configured to hold a supply of resin, and a build surface disposedinside the vat. The system may also include a print head configured todischarge a matrix-coated continuous reinforcement onto the buildsurface, and an energy source configured to expose resin on a surface ofthe matrix-coated continuous reinforcement to a cure energy.

In another aspect, the present disclosure is directed to a method ofadditively manufacturing a composite structure. The method may includedischarging from a print head a matrix-coated continuous reinforcementonto a build surface, and submerging the matrix-coated continuousreinforcement in resin. The method may also include exposing resin at asurface of the matrix-coated continuous reinforcement to a cure energy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic illustration of an exemplary disclosed additivemanufacturing system; and

FIG. 2 is a diagrammatic illustration of another exemplary disclosedadditive manufacturing system.

DETAILED DESCRIPTION

FIG. 1 illustrates an exemplary system 10, which may be used tocontinuously manufacture a composite structure 12 having any desiredcross-sectional shape (e.g., circular, polygonal, etc.). System 10 mayinclude at least a vat 14, a support 16, a head 18, and an energy source20. Vat 14 may be a vessel that is configured to hold a supply of resin(e.g., a photopolymer resin), from which at least a portion (e.g., asurface coating) of structure 12 is to be fabricated. Head 18 may becoupled to and moved by support 16 to fabricate at least a portion(e.g., an internal skeleton) of structure 12 within vat 14. In thedisclosed embodiment of FIG. 1, support 16 is a robotic arm capable ofmoving head 18 in multiple directions during fabrication of structure12. Energy source 20 may be configured to selectively expose resin invat 14 that coats the structural skeleton fabricated by head 18, therebycausing the resin to cure and form a hardened coating on the skeleton.

Head 18, itself, may be configured to receive or otherwise contain amatrix. The matrix may include any type of material (e.g., a liquidresin, such as a zero-volatile organic compound resin; a powdered metal;etc.) that is curable. Exemplary matrixes include thermosets, single- ormulti-part epoxy resins, polyester resins, cationic epoxies, acrylatedepoxies, urethanes, esters, thermoplastics, photopolymers, polyepoxides,thiols, alkenes, thiol-enes, and more. In one embodiment, the matrixinside head 18 may be pressurized, for example by an external device(e.g., an extruder or another type of pump—not shown) that is fluidlyconnected to head 18 via a corresponding conduit (not shown). In anotherembodiment, however, the matrix pressure may be generated completelyinside of head 18 by a similar type of device. In yet other embodiments,the matrix may be gravity-fed through and/or mixed within head 18. Insome instances, the matrix inside head 18 may need to be kept cooland/or dark to inhibit premature curing; while in other instances, thematrix may need to be kept warm for the same reason. In eithersituation, head 18 may be specially configured (e.g., insulated,chilled, and/or warmed) to provide for these needs.

The matrix may be used to coat, encase, or otherwise at least partiallysurround any number of continuous reinforcements (e.g., separate fibers,tows, rovings, ribbons, and/or sheets of material) and, together withthe reinforcements, make up at least a portion (e.g., a wall) ofcomposite structure 12. The reinforcements may be stored within (e.g.,on separate internal spools—not shown) or otherwise passed through head18 (e.g., fed from external spools). When multiple reinforcements aresimultaneously used, the reinforcements may be of the same type and havethe same diameter and cross-sectional shape (e.g., circular, square,flat, etc.), or of a different type with different diameters and/orcross-sectional shapes. The reinforcements may include, for example,carbon fibers, vegetable fibers, wood fibers, mineral fibers, glassfibers, metallic wires, optical tubes, etc. It should be noted that theterm “reinforcement” is meant to encompass both structural andnon-structural types of continuous materials that can be at leastpartially encased in the matrix discharging from head 18.

The reinforcements may be exposed to (e.g., coated with) the matrixwhile the reinforcements are inside head 18, while the reinforcementsare being passed to head 18 (e.g., as a prepreg material), and/or whilethe reinforcements are discharging from head 18, as desired. The matrix,dry reinforcements, and/or reinforcements that are already exposed tothe matrix (e.g., wetted reinforcements) may be transported into head 18in any manner apparent to one skilled in the art.

The matrix and reinforcement may be discharged from head 18 via at leasttwo different modes of operation. In a first mode of operation, thematrix and reinforcement are extruded (e.g., pushed under pressureand/or mechanical force) from head 18, as head 18 is moved by support 16to create the 3-dimensional shape of structure 12. In a second mode ofoperation, at least the reinforcement is pulled from head 18, such thata tensile stress is created in the reinforcement during discharge. Inthis mode of operation, the matrix may cling to the reinforcement andthereby also be pulled from head 18 along with the reinforcement, and/orthe matrix may be discharged from head 18 under pressure along with thepulled reinforcement. In the second mode of operation, where the matrixis being pulled from head 18, the resulting tension in the reinforcementmay increase a strength of structure 12, while also allowing for agreater length of unsupported material to have a straighter trajectory(i.e., the tension may act against the force of gravity to providefree-standing support for structure 12).

The reinforcement may be pulled from head 18 as a result of head 18moving away from a build surface 22. In particular, at the start ofstructure-formation, a length of matrix-impregnated reinforcement may bepulled and/or pushed from head 18, deposited onto a build surface 22within vat 14, and cured, such that the discharged material adheres tobuild surface 22. Thereafter, head 18 may be moved away from buildsurface 22, and the relative movement may cause the reinforcement to bepulled from head 18. It should be noted that the movement of thereinforcement through head 18 could be assisted (e.g., via internal feedmechanisms), if desired. However, the discharge rate of thereinforcement from head 18 may primarily be the result of relativemovement between head 18 and build surface 22, such that tension iscreated within the reinforcement. It is contemplated that build surface22 could be moved away from head 18 instead of or in addition to head 18being moved away from build surface 22.

One or more cure enhancers (e.g., one or more light sources, anultrasonic emitter, a laser, a heater, a catalyst dispenser, a microwavegenerator, etc.) 24 may be mounted proximate (e.g., on and/or trailingfrom) head 18 and configured to enhance a cure rate and/or quality ofthe matrix as it is discharged from head 18. Cure enhancer 24 may becontrolled to selectively expose internal and/or external surfaces ofstructure 12 to energy (e.g., light energy, electromagnetic radiation,vibrations, heat, a chemical catalyst or hardener, etc.) during theformation of structure 12. The energy may increase a rate of chemicalreaction occurring within the matrix, sinter the material, harden thematerial, or otherwise cause the material to cure as it discharges fromhead 18.

During the fabrication of structure 12 by head 18, the internal skeletonmay be incrementally submerged within the resin of vat 14. For example,after fabrication of each horizontal layer of structure 12, the level ofthe resin in vat 14 may be raised by a height of the new layer. Thelevel of resin in vat 14 may be regulated by selectively allowing (e.g.,by opening and closing a valve 26) additional resin to enter vat 14 froma supply 28.

After the raising of the resin level within vat 14, energy source 20 maybe selectively regulated to cause curing of the resin that coats the newlayer of structure 12. Energy source 20 may be, for example, a UV lightprojector, a laser, an electron beam emitter, and/or another source thatis controlled to expose select surfaces of only the new layer ofstructure 12 that was just fabricated by head 18.

It should be noted that energy source 20 and cure enhancer(s) 24 mayproduce the same type and magnitude of cure energy, or different typesand magnitudes of cure energy, as desired. In one exemplary embodiment,energy source 20 is an array of lasers (e.g., at least three differentblue lasers) that focus light energy having a wavelength of about430-470 nm together at particular points within vat 14 to cause nearlyinstantaneous solidification and curing of the resin within vat 14. Inthis same embodiment, one or more UV lights may function as cureenhancers 24, to expose the matrix to light having a wavelength of about365-405 nm. In other embodiments, combinations of acoustic energy, heat,and/or light may be used together, if desired.

In some applications, care should be taken to avoid oxygen-exposure ofthe matrix inside the composite material of structure 12, prior tocoating of the new layer with cured resin from vat 14. In theseapplications, a shield gas (e.g., an inert gas such as argon, helium,nitrogen, etc.) may be directed from a gas supply 30 into vat 14, in anamount sufficient to create a barrier 32 over structure 12.

A controller 34 may be provided and communicatively coupled with support16, head 18, energy source 20, cure enhancers 24, valve 26, and/or gassupply 30. Controller 34 may embody a single processor or multipleprocessors that include a means for controlling an operation of system10. Controller 34 may include one or more general- or special-purposeprocessors or microprocessors. Controller 34 may further include or beassociated with a memory for storing data such as, for example, designlimits, performance characteristics, operational instructions, matrixcharacteristics, reinforcement characteristics, characteristics ofstructure 12, and corresponding parameters of each component of system10. Various other known circuits may be associated with controller 34,including power supply circuitry, signal-conditioning circuitry,solenoid/motor driver circuitry, communication circuitry, and otherappropriate circuitry. Moreover, controller 34 may be capable ofcommunicating with other components of system 10 via wired and/orwireless transmission.

One or more maps may be stored in the memory of controller 34 and usedduring fabrication of structure 12. Each of these maps may include acollection of data in the form of models, lookup tables, graphs, and/orequations. In the disclosed embodiment, the maps are used by controller34 to determine desired characteristics of energy source 20, cureenhancers 24, the associated matrix and resin, and/or the associatedreinforcements at different locations within structure 12. Thecharacteristics may include, among others, a type, quantity, and/orconfiguration of reinforcement, matrix, and/or resin to be discharged ata particular location within structure 12; an amount, intensity, shape,and/or location of desired curing; and/or a location and thickness ofany surface coatings to be generated by energy source 20. Controller 34may then correlate operation of support 16 (e.g., the location and/ororientation of head 18), the discharge of material from head 18 (a typeof material, desired performance of the material, cross-linkingrequirements of the material, a discharge rate, etc.), the operation ofenergy source 20, the operation of cure enhancers 24, and/or theoperation of valve 26, such that structure 12 is produced in a desiredmanner.

Another embodiment of system 10 is disclosed in FIG. 2. Like theembodiment of FIG. 1, system 10 of FIG. 2 may also include vat 14,support 16, head 18, and energy source 20. However, in contrast to FIG.1, system 10 of FIG. 2 may include an additional support 36 that isconnected to move build surface 22. In this embodiment, the level ofresin within vat 14 may remain substantially constant, and support 36may be selectively activated by controller 34 to incrementally lowerbuild surface 22 and structure 12 into the resin after fabrication ofeach new layer of structure 12 by head 18. Support 36 may take any formknown the art, for example an elevator having an external motor 38 thatis connected to the end of a lead screw 40, and one or more brackets 42transforming a rotation of lead screw 40 into a lowering of buildsurface 22.

In one example, build surface 22 may be at least partially transparentand/or perforated. The partially transparent surface may allow for cureenergy from a second energy source 20 (e.g., a source located belowbuild surface 22) to pass through build surface 22 and expose a lowerend of structure 12. The perforated nature of build surface 22 may allowfor resin to flow from a lower section of vat 14 to an upper section, byway of build surface 22, during lowering of building surface 22.

Also in contrast to the embodiment of FIG. 1, support 16 may take adifferent form. For example, support 16 may embody a gantry that islocated at an upper end of vat 14. In this embodiment, support 16 mayfunction to only move head 18 transversely (e.g., in X- andY-directions). It is contemplated, however, that support 16 could haveanother configuration (e.g., a hybrid gantry/arm configuration), ifdesired.

INDUSTRIAL APPLICABILITY

The disclosed system may be used to continuously manufacture compositestructures having any desired cross-sectional size, shape, length,density, strength and/or surface texture. The composite structures mayinclude any number of different reinforcements of the same or differenttypes, diameters, shapes, configurations, and consists, each coated witha common matrix and/or resin. Operation of system 10 will now bedescribed in detail.

At a start of a manufacturing event, information regarding a desiredstructure 12 may be loaded into system 10 (e.g., into controller 34 thatis responsible for regulating operations of system 10). This informationmay include, among other things, a size (e.g., diameter, wall thickness,length, etc.), a contour (e.g., a trajectory), surface features (e.g.,ridge size, location, thickness, length; flange size, location,thickness, length; etc.) and finishes, connection geometry (e.g.,locations and sizes of couplings, tees, splices, etc.),location-specific matrix stipulations, location-specific reinforcementstipulations, etc. It should be noted that this information mayalternatively or additionally be loaded into system 10 at differenttimes and/or continuously during the manufacturing event, if desired.Based on the component information, one or more different reinforcementsand/or matrixes may be selectively installed and/or continuouslysupplied into head 18, and vat 14 may be filled with a specific amountand/or type of resin.

Installation of the reinforcement may be performed by passing thereinforcements down through print head 18. Installation of the matrixmay include filling head 18 with matrix and/or coupling of an extruder(not shown) to head 18. Head 18 may then be moved by support 16 underthe regulation of controller 34 to cause matrix-coated reinforcements tobe placed against or on a corresponding build surface 22. Cure enhancers24 within head 18 may then be selectively activated to cause hardeningof the matrix surrounding the reinforcements, thereby bonding thereinforcements to build surface 22.

The component information may then be used to control operation ofsystem 10. For example, the reinforcements may be pulled and/or pushedfrom head 18 (along with the matrix), while support 16 selectively moveshead 18 in a desired manner during exposure of the matrix-coatedreinforcement to cure energy, such that an axis of the resultingstructure 12 follows a desired trajectory.

In some situations, an outer coating on structure 12 may be beneficial.The outer coating may provide, for example, a desired surface texture(e.g., smoothness), a desired property (e.g., hardness, conductivity,etc.), or a desired appearance (e.g., sheen) that cannot be created viathe discharge of matrix-coated reinforcement from head 18 alone.

As each layer of matrix-coated reinforcement is deposited by head 18 andcured, controller 34 may cause the layer to be selectively coated withresin from vat 14 (e.g., by increasing the resin level or by loweringbuild surface 22 incrementally). Thereafter, one or more of energysources 20 may be situated to flash a pattern onto the just-submersedlayer of structure 12 (e.g., from above, below, and/or a side ofstructure 12), thereby causing the resin in vat 14 to solidify at thesurface of the submersed layer.

It is contemplated that, rather than the outer coating described abovebeing applied layer-by-layer, as head 18 creates structure 12, the outercoating could be applied after all of structure 12 has been created. Forexample, the completed structure 12 may be lowered into vat 14 (e.g.,all at once or one level at a time), and a desired pattern flashed onthe completed outer surface of structure 12 to create the coating. Thepattern may be flashed layer-by-layer onto the completed surface ofstructure 12, or flashed all at once, as desired. It should also benoted that the coating processes of FIGS. 1 and 2 may be used for morethan coating structure 12. That is, the processes may allow entirely newfeatures to extend from and/or built on top of structure 12, albeitstructures without fiber-reinforcement. In addition, it may be possiblefor layers of matrix-coated reinforcement to be interleaved with anynumber of adjacent layers of only cured resin, if desired. Oncestructure 12 has grown to a desired length, structure 12 may bedisconnected (e.g., severed) from head 18 in any desired manner.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the disclosed additivemanufacturing system. Other embodiments will be apparent to thoseskilled in the art from consideration of the specification and practiceof the disclosed additive manufacturing system. It is intended that thespecification and examples be considered as exemplary only, with a truescope being indicated by the following claims and their equivalents.

What is claimed is:
 1. A method of additively manufacturing a compositestructure, comprising: discharging from a print head a matrix-coatedcontinuous reinforcement onto a build surface; submerging thematrix-coated continuous reinforcement in resin; exposing resin at asurface of the matrix-coated continuous reinforcement to a cure energy;and exposing a matrix in the matrix-coated continuous reinforcement tocure energy to at least partially cure the matrix prior to submergingthe matrix-coated continuous reinforcement in resin.
 2. The method ofclaim 1, further including incrementally lowering the matrix-coatedcontinuous reinforcement into the resin.
 3. The method of claim 2,further including passing resin through the build surface duringincremental lowering of the matrix-coated continuous reinforcement. 4.The method of claim 2, further including incrementally raising a levelof resin inside a vat housing the build surface.
 5. The method of claim4, further including moving the print head inside the vat.
 6. The methodof claim 1, further including interleaving cured layers of thematrix-coated continuous reinforcement with cured layers of the resin.7. A method of additively manufacturing a composite structure,comprising: discharging from a print head a matrix-coated continuousreinforcement onto a build surface; submerging the matrix-coatedcontinuous reinforcement in resin; exposing resin at a surface of thematrix-coated continuous reinforcement to a cure energy; and at leastpartially curing all of the matrix-coated continuous reinforcement priorto curing of any resin on the surface of the matrix-coated continuousreinforcement.
 8. The method of claim 1, wherein exposing resin at thesurface of the matrix-coated continuous reinforcement to the cure energyincludes directing the cure energy through the build surface.
 9. Themethod of claim 1, further including generating an oxygen inhibitingbarrier at a surface of the resin.
 10. A method of additivelymanufacturing a composite structure, comprising: discharging from amatrix-coated continuous reinforcement onto a build surface; at leastpartially submerging the matrix-coated continuous reinforcement inresin; curing the resin; and exposing a matrix in the matrix-coatedcontinuous reinforcement to cure energy to at least partially cure thematrix prior to at least partially submerging the matrix-coatedcontinuous reinforcement in resin.
 11. The method of claim 10, whereinexposing the matrix to cure energy includes directing light into thematrix.
 12. The method of claim 10, further including incrementallylowering the matrix-coated continuous reinforcement into the resin. 13.The method of claim 12, further including passing resin over the buildsurface during incremental lowering of the matrix-coated continuousreinforcement.
 14. The method of claim 10, further includingincrementally raising a level of resin inside a vat housing the buildsurface.
 15. The method of claim 10, further including interleavingcured layers of the matrix-coated continuous reinforcement with curedlayers of the resin.
 16. A method of additively manufacturing acomposite structure, comprising: discharging from a matrix-coatedcontinuous reinforcement onto a build surface; at least partiallysubmerging the matrix-coated continuous reinforcement in resin; curingthe resin; and at least partially curing all of the matrix-coatedcontinuous reinforcement prior to curing of any resin.
 17. The method ofclaim 10, wherein curing resin includes directing cure energy throughthe build surface.
 18. The method of claim 17, wherein the cure energyis UV light.
 19. The method of claim 10, further including generating anoxygen inhibiting barrier at a surface of the resin.